1. Field of the Invention
The present invention relates to a motor and a mechanism, and in particular relates to a motor and a mechanism having the function of increasing or decreasing a brake torque.
2. Description of Related Art
To lock output axes of motors in cases of emergency stops or power failures, the motors are generally equipped with holding brakes that are operated without excitation (for example, Japanese Unexamined Patent Publication (Kokai) No. 2005-54843). Constant and high brake torque is required of the holding brakes. Thus, the holding brakes can supply holding torque required to lock the output axes, even when the holding brakes are not energized. For example, when the motors are used for driving joints of robots, the holding brakes serve to support the self-weight of the robots, even in cases of emergency stops or power failures, thus allowing maintaining the posture of the robots.
FIG. 1 is a block diagram of a conventional motor having a holding brake inside the motor. A motor 1000 includes an output axis 1001 and a holding brake (hereinafter also simply called “brake”) 1002. To the brake 1002, only a brake operation signal is inputted from a controller 1004 disposed outside the motor 1000. A brake torque is constant at this time.
FIG. 2 is a block diagram of a conventional mechanism of a robot in which a holding brake is disposed outside a motor (inside a decelerator, between an arm and the decelerator, or the like). A mechanism 2000 includes an output axis 1001A, a brake 1002A, and a decelerator 1006. A motor 1000A is disposed in a first arm 1007. The mechanism 2000 is disposed between the first arm 1007 and a second arm 1008. To the brake 1002A, only a brake operation signal is inputted from a controller 1004A disposed outside the mechanism 2000. A brake torque is constant at this time.
In the conventional art, since the brake torque of the holding brake is constant and high, the output axis of the motor cannot be easily rotated during operation of the brake, even if an external torque is applied to the output axis of the motor. Also in the case of the robot, as a matter of course, the robot cannot be easily moved (the posture of the robot cannot be changed) during operation of the holding brake of the motor, even if a person pushes the arms of the robot. Thus, when the robot is stopped during operation and the motor cannot be driven, the robot cannot be moved from the posture at the time of stopping.
Conventionally, when motors are stopped in cases of emergency stops, power failures, or the like, brakes lock the rotation of output axes of the motors. At this time, the following equation holds true during operation of the brakes.
Brake torque (constant value) Tb>>Holding torque Th of output axis
wherein, “holding torque Th of output axis” represents torque required to lock the output axes of the motors.
Since brake torque Tb is sufficiently high, people cannot rotate the output axes during operation of the brakes. The motors having this configuration are often used for driving joints of robots in general, and therefore when the motors are stopped under the application of the brakes, it is not easy for the people to move arms of the robots by pushes on the arms.